Customer has a Sonicwall router connected to high speed internet, tested at 30Mbps down 11Mbps Up. I don't remember the hand-off from the ISP.

Another 3rd party service got involved saying that the connection to their cloud service is slow because the WAN port on the Sonicwall is not configured correctly. This other guy does not work for the ISP.

X1 WAN port set to Auto Negotiate. Status shows 100Mbps Full Duplex.
This other company's tech says this needs to be set to 100Mbps Full Duplex, but not Auto Negotiate.

I made the change off hours. The speed dropped in half. Multiple tests max out at 18Mbps down when set this way. When set back to Auto, speed jumps back to 30Mbps.

Does this prove that Auto Negotiate should be set for this port?